Objects are fabricated by using additive techniques or subtractive techniques or a combination of additive and subtractive techniques. Additive techniques involve adding material to a workpiece, and, conversely, subtractive techniques involve removing material from a workpiece. When a sculptor is working with clay and adds bits of clay to the inchoate statue, the sculptor is employing an additive technique, but when the sculptor scrapes away excess clay with a rasp or riffler, the sculptor is employing a subtractive technique.
One class of manufacturing that is colloquially known as “3D printing” and “additive manufacturing” endeavors to fabricate a three-dimensional object from a mathematical model of the object using additive techniques and by avoiding, or minimizing the use of, subtractive techniques.
Perhaps the greatest advantage of additive manufacturing is that it can build an object of any shape. Furthermore, a machine can build an object of any shape without changing any hardware (e.g., molds, dies, mandrels, etc.). To accomplish this, however, there is the constraint that each incremental portion of material must be deposited on:                (i) the workpiece, which consists of previously deposited portions of material,        (ii) a build platform, which supports the workpiece, or        (iii) a scaffold of support material that is temporary and not part of the final object.In other words, a portion of material cannot be deposited on air.        
There are, however, costs and disadvantages associated with traditional additive manufacturing.